The invention relates to a method of processing zirconium based material and more particularly to a method of controlling creep in a zirconium-niobium-tin-iron alloy.
In the development of nuclear reactors, such as pressurized water reactors and boiling water reactors, fuel designs impose significantly increased demands on all of the core components, such as cladding, grids, guide tubes, and the like. Such components are conventionally fabricated from the zirconium-based alloys, Zircaloy-2 and Zircaloy-4. Increased demands on such components will be in the form of longer required residence times and thinner structural members, both of which cause potential corrosion and/or hydriding problems. These increased demands have prompted the development of alloys that have improved corrosion and hydriding resistance, as well as fabricability and mechanical properties that are typical of the conventional Zircaloys. One such class of materials are the zirconium alloys containing zirconium, niobium, tin, and a third element, such as a zirconium alloy containing 1 percent by weight niobium, 1 percent by weight tin, and at least 0.15 percent by weight iron. Alloys of zirconium, niobium, tin and iron which have been proposed include those of Castaldelli et al. (Long-term Test Results of Promising New Zirconium Alloys," Zirconium in the Nuclear Industry, 5th Conference, ASTM STP 754, 1982, pages 105-126) who tested a zirconium 1Nb-1Sn-0.5 Fe alloy and mention a zirconium 1Nb-1Sn alloy with 0.15-0.20 Fe, and an alloy known as Ozhennite 0.5, which comprises 0.18-0.22 wt. % Sn, 0.09-0.11 wt. % Nb, 0.09-0.11 wt. % Fe, and 0.09-0.11 wt. % Ni, all alloyed with Zr.
U.S. Pat. No. 4,649,023, issued Mar. 10, 1987 (hereinafter "the ZIRLO patent") is a composition and process patent, generally covering a composition range of 0.5-2.0 w/o (weight percent) Nb, 0.9-1.5 w/o Sn, and 0.09-0.11 w/o of third element selected from Fe, Cr, Mo, V, Cu, Ni and W, (or presumably 0.09-0.11 w/o of mixtures of more that one such "third element") and generally with annealing temperatures between cold working stages in the range of 932.degree.-1202.degree. F. That patent does not address controlling thermal creep.
Different creep rates are desirable for different applications. Low creep rates are generally thought to be desirable for spacer material and water rods, for example, but it may be desirable for higher creep in fuel rods to compensate for the fuel pellet expansion which occurs over the operating life of the fuel. There has never, heretofore, been a straightforward method of controlling creep in such alloys.